Configurable interface circuit
Patent Information
- Application Number
- CN202411756535.1
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Priority Date
- 2024-01-24
- Filing Date
- 2024-12-03
- Publication Date
- 2025-07-25
Smart Images
Figure CN120377889A_ABST
Abstract
Description
Technical Field
[0001] The present disclosure relates to a configurable interface circuit configured to measure analog and digital currents when operating in analog and digital modes. Background Art
[0002] Electronic modules can be used to facilitate the monitoring or control of applications such as chemical or industrial process control, motion control, building control, etc., such as the control of heating, ventilation, and air conditioning (HVAC). Such modules can have a hardware interface that provides a current or voltage output, as well as separate inputs, for example for monitoring current, voltage, or resistance (e.g., for measurements using a resistance temperature device (RTD)). The electronic module can provide signal conditioning, for example including one or more filtering or protection devices, and can provide analog-to-digital conversion capabilities. Summary of the Invention
[0003] In a first aspect of the present disclosure, there is provided a configurable interface circuit that supports alternative operating modes, including an analog mode and a digital mode. The interface circuit includes: device terminals that can be coupled to an external field device; a digital current path coupled to the device terminals, where the digital current path includes a digital sense resistor having a first terminal coupled to the device terminals; an analog current path including an analog sense resistor having a first terminal coupled to the first terminal of the digital sense resistor; and a measurement circuit including: a first input terminal coupled to a second terminal of the digital sense resistor; and a second input terminal coupled to a second terminal of the analog sense resistor. When the configurable interface circuit operates in the analog mode, an analog current can flow through the analog current path and the device terminals, and the measurement circuit is configured to measure an analog signal by measuring the voltage between the first input terminal and the second input terminal. When the configurable interface circuit operates in the digital mode, a digital current is controlled to flow through the digital current path and the device terminals, and the measurement circuit is configured to measure the voltage between the first input terminal and the second input terminal to measure a digital signal.
[0004] In a second aspect of the present disclosure, a method for operating a configurable interface circuit in any one of a plurality of selectable operating modes, including an analog mode and a digital mode, is provided, where the configurable interface circuit includes: device terminals that can be coupled to an external field device; a digital current path coupled to the device terminals, where the digital current path includes a digital sense resistor having a first terminal coupled to the device terminals; an analog current path including an analog sense resistor having a first terminal coupled to the first terminal of the digital sense resistor; and a measurement circuit including: a first input terminal coupled to a second terminal of the digital sense resistor; and a second input terminal coupled to a second terminal of the analog sense resistor, where the method includes: when the configurable interface circuit operates in the analog mode and an analog current can flow through the analog current path: measuring an analog signal by the measurement circuit by measuring a voltage between the first input terminal and the second input terminal, and when the configurable interface circuit operates in the digital mode and a digital current can flow through the digital current path: measuring a digital signal by measuring a voltage between the first input terminal and the second input terminal by the measurement circuit.
[0005] In a third aspect of the present disclosure, an interface circuit supporting multiple selectable operating modes is provided, the interface circuit including: device terminals that can be coupled to an external field device; a first current path coupled to the device terminals, where the first current path includes a first sense resistor having a first terminal coupled to the device terminals; and a second current path including a second sense resistor having a first terminal coupled to the first terminal of the first sense resistor; where when the interface circuit operates in a first mode and a first current can flow through the first current path, the interface circuit is configured to measure a first signal by measuring a voltage between a second terminal of the first sense resistor and a second terminal of the second sense resistor, and where when the interface circuit operates in a second mode and a second current can flow through the second current path, the interface circuit is configured to measure a second signal by measuring a voltage between a second terminal of the first sense resistor and a second terminal of the second sense resistor. BRIEF DESCRIPTION OF THE DRAWINGS
[0006] As an example only, aspects of the present disclosure are described with reference to the following schematic diagrams, where:
[0007] Figure 1 An example of a configurable interface circuit is shown;
[0008] Figure 2 Another example of a configurable interface circuit is shown;
[0009] Figure 3 shows the optional additional features of the configurable interface circuit of Figure 2 ;
[0010] Figure 4 shows the exemplary additional details implemented by the configurable interface circuit of Figure 3 ;
[0011] Figure 5 illustrates an example of a configurable interface circuit according to one aspect of the present disclosure;
[0012] Figure 6 shows a representation of the configurable interface circuit when operating in analog current mode Figure 5 ;
[0013] Figure 7 shows a representation of the configurable interface circuit when operating in digital output mode Figure 5 ;
[0014] Figure 8 shows an example of a configurable interface circuit according to another aspect of the present disclosure when operating in digital output mode;
[0015] Figure 9 shows the details of an exemplary implementation of the configurable interface circuit of Figure 5 ; DETAILED DESCRIPTION
[0016] As explained in more detail below, the configurable interface circuit generally includes a variety of different modes, including one or more analog modes and one or more digital modes. The interface circuit generally includes functions for measuring analog current and / or voltage during analog mode operation, but does not include digital current and / or voltage. For many application spaces, this is sufficient, but it has been recognized that measuring current and / or voltage during digital mode operation may be useful for diagnostic purposes and the like.
[0017] The present disclosure relates to a configurable interface circuit equipped with analog and digital signal measurement capabilities. By adding an additional sense resistor in the digital current path, digital signal capabilities are added to an existing circuit at the lowest cost. A measurement circuit that may include an ADC is configured to measure the voltage across the sense resistor in the digital current path and across the pre-existing sense resistors in the analog current path. During digital mode operation, no (or negligible) current flows through the analog current path, so the measured value corresponds to the voltage across the sense resistor in the digital current path. During analog mode operation, no (or negligible) current flows through the digital current path, so the measured value corresponds to the voltage across the sense resistor in the analog current path. Thus, due to the inclusion of the sense resistor in the digital current path, both digital and analog current / voltage can be measured by the same measurement circuit without any changes to the measurement circuit, which is a very low-cost and low-complexity component. Thus, the additional functionality of digital signal measurement is added efficiently and economically.
[0018] Figure 1 An example generally showing a configurable interface circuit 100 is presented. The interface circuit may include a configurable drive circuit 104 and a configurable measurement circuit 106, where the interface circuit 100 may be coupled to one or more field devices, such as field device 130. The use of the phrase "field device" generally may refer to one or more of actuators, sensors, or other devices. The field device 130 does not need to be located at a specific distance from the interface circuit 100, but will typically be located remotely relative to the interface circuit 100. The field device may be coupled to the interface circuit 100, for example, using one or more screw terminals or other electrical interconnections, such as including a first device terminal 120A and a second device terminal 120B. In one example, the second device terminal 120B may be shared among multiple field devices as a ground or common terminal (which may be ground or any other suitable common reference voltage). The interface circuit 100 may include an integrated circuit package 102, such as having one or more monolithic integrated circuits housed with the package 102. The combination of the configurable drive circuit 104 and the configurable measurement circuit 106 may define a configurable channel, and the interface circuit 100 may include multiple channels, for example, implemented within the integrated circuit package 102.
[0019] In one example, one or more of configurable drive circuit 104, configurable measurement circuit 106, and control circuit 108 may be integrally combined in a shared monolithic integrated circuit. As an illustrative example, control circuit 108 may include one or more of a state machine, a microcontroller architecture, a general-purpose processor circuit, or may include one or more configurable logic devices. A digital interface 114 may be provided, for example, to provide one or more of a serial or parallel communication interface. Configuration information of interface circuit 100 may be provided, for example, via digital interface 114 and may be used by control circuit 108 to select an operating mode in interface circuit 100, for example, by enabling or disabling various functional elements included in one or more of configurable drive circuit 104 or configurable measurement circuit 106.
[0020] Integrated circuit package 102 may include one or more pins to allow application flexibility of interface circuit 100. For example, configurable drive circuit 104 may be coupled to output pin 116A. A first node of sense resistor 112 may be coupled between output pin 116A and a second pin 116B, such as where second pin 116B is coupled to measurement circuit 106. Alternatively or additionally, sense resistor 112 may be located inside integrated circuit package 102. Measurement circuit 106 may also be coupled to a third pin 116C, such as to a second node of sense resistor 112, such that measurement circuit 106 may monitor a voltage drop across sense resistor 122. In an illustrative example, sense resistor 112 may contribute to a total impedance presented by interface circuit 100 to device terminals 120A and 120B. Configurable drive circuit 104 may optionally include optional impedance circuit 110 to vary an input impedance presented by interface circuit 100. As an illustrative example, interface circuit 100 may support at least two optional impedances, including a controlled impedance mode and a lower impedance mode. The controlled impedance mode may provide a specified impedance range, for example, to allow digital communication on a channel including conductors coupled to device terminals 120A and 120B, for example, simultaneously with other stimuli, measurements, or a combination of stimuli and measurements on the channel.
[0021] Figure 2 Another example configurable interface circuit 200 is shown, which is similar to Figure 1 circuit 100, with the same reference numerals representing like features. It represents a single-channel circuit, and it will be understood that it may optionally include one or more copies of the represented circuit, such that configurable interface circuit 200 includes multiple channels. Although Figure 2 not shown, it may also include reference Figure 1The control circuit 108 described above is used to select and control the operating mode. The configurable interface circuit 200 supports multiple selectable operating modes. For example, since the drive circuit 104 is software-configurable. Some example operating modes are described below. This enables the end user to use the same configurable interface circuit 200 for multiple different functions.
[0022] In this example, the configurable drive circuit 104 includes a digital control circuit 210 for controlling digital signals and an analog control circuit 220 for controlling analog signals. The configurable interface circuit 200 also includes a digital current path formed by a switch 232 and a diode 234. In this example, the switch 232 is a p-type FET. It should be understood that the p-type FET is merely an example of a controllable switch, and the switch 232 can alternatively include any other type of transistor, such as an n-type FET, an n-type or p-type bipolar transistor, an n-type or p-type IGBT, a relay switch, etc. The digital control circuit 210 is configured to control the state of the switch 232 to control the digital current that can flow through the digital current path. In Figure 1 the example, the digital control circuit 210 is configured to control the voltage at the gate of the transistor 232 to control whether the transistor 232 is in the on state or the off state. For example, the digital control circuit 210 can turn on the transistor to place the switch 232 in the closed state and allow current to flow from the external power supply 240 through the digital current path and the device terminal 120A to the field device 130. It can also turn off the transistor to place the switch 232 in the open state and stop the current flow through the digital current path and the device terminal 120A. In this way, the supply of digital current to the field device 130 can be controlled. It should also be understood that this may generate a corresponding digital voltage at the device terminal 120A (depending on the nature of the field device 130), so this operation can be regarded as a digital current / voltage output. In an alternative, the circuit can be configured to receive digital current from the field device (i.e., absorb rather than supply digital current), for example, by changing the external power supply 240, the type of transistor for the switch 232, and the direction of the diode 234. In this case, the digital current will flow through the digital current path in the opposite direction and can thus be regarded as a negative current. In any case, the digital control circuit 210 is controlling the digital current / voltage.
[0023] The analog control circuit 220 is coupled to the sense resistor 112. It can be configured to operate selectively in one or more different analog modes, examples of which are described below. In an example, it is configured to control an analog current through the sense resistor 112 such that the analog current flows through the sense resistor 112 and the device terminal 120A to / from the field device 130. This mode of operation can be referred to as the analog output current mode, regardless of the direction of the current, because the current is controlled by the analog control circuit 220. In another example mode of operation, it can be configured to source or sink an analog current controlled by the field device 130, which flows through the device terminal 120A and the sense resistor 112. This mode of operation can be referred to as the analog input current mode, regardless of the direction of the current, because the current is controlled by something other than the analog control circuit 220, such as the field device 130. In another example mode of operation, it can be configured to drive an analog output voltage at the output of the analog control circuit 220, which in turn affects the voltage at the device terminal 120 and may cause an analog current to flow through the analog current path. At the first device terminal 120A, the driven analog voltage can be positive or negative, and in any case, this can be referred to as the analog output voltage mode, because the voltage is controlled by the analog control circuit 220. In another example mode of operation, it can be configured to allow another device / entity, such as the field device 130, to drive a voltage at the first device terminal 120A, which may cause an analog current to flow through the analog current path. At the first device terminal 120A, the driven analog voltage can be positive or negative, and in any case, this can be referred to as the analog input voltage mode, because the voltage is controlled by something other than the analog control circuit 220.
[0024] Accordingly, the configurable interface circuit 200 can be configured for alternative modes of operation including a digital mode for controlling digital current / voltage and an analog mode (which can include an analog output current mode and / or an analog input current mode and (or) an analog output voltage mode and (or) an analog input voltage mode). During the digital mode, the configurable drive circuit 104 operates such that the digital control circuit 210 controls the digital current / voltage as described above, and the analog control circuit 220 is disabled. During the analog mode, the configurable drive circuit 104 operates in any of the ways described above, and the digital control circuit 210 holds the switch 232 in the open state.
[0025] During the simulation mode, optionally, the measurement circuit 106 may be configured to simultaneously measure analog signals (e.g., analog current and / or analog voltage), for example, by measuring the voltage across the sense resistor 112. For example, the measurement circuit 106 may include an analog-to-digital converter ADC that is coupled to pins 116B and 116C and is configured to digitally convert the voltage across the sense resistor 112, which voltage itself may represent a useful measurement of the analog voltage (or be operationally useful for deriving some other analog voltage value, e.g., the voltage at the first device terminal 120A if the analog control circuit 220 knows the voltage at pin 116B, for example, because it is held at a reference voltage such as ground, or because the analog control circuit 220 drives it to a specific voltage). Additionally or alternatively, the measured voltage across the sense resistor 112 can be used to determine a measurement of the analog current flowing through the resistor (based on knowledge of the value of the sense resistor 112). If the analog control circuit 220 is operating in an analog output current mode, the measurement of the analog current can optionally be used by the analog control circuit 220 for closed-loop feedback control of the analog current. During the analog output voltage mode, the analog control circuit 220 can optionally use the measured value of the analog voltage across the sense resistor 112, or the analog voltage measurement at pin 116C in a single-ended example, for closed-loop feedback control of the voltage, in order to compensate for the voltage drop across the sense resistor 112 by adjusting the controlled output voltage, thereby providing a compensated voltage to the field device 130. Further, optionally, although not shown for simplicity in Figure 2 the analog control circuit 220 may be coupled to pin 116C (optionally also coupled to pin 116B), for example, to provide feedback regarding the analog current and / or voltage at the first device terminal 120A. In this example, the feedback may not be a detailed measurement of the current and / or voltage magnitude (as determined by the measurement circuit 106), but rather can be used to determine whether the feedback signal is too high or too low relative to a reference value, which will indicate whether the current and / or voltage driven by the analog control circuit 220 is too high or too low (e.g., as in the detailed example described later in Figure 9 .
[0026] Figure 3Shows an optional additional feature of the configurable interface circuit 200, which has a short - circuit clamping safety function. To this end, the digital current path also includes a safety resistor 310, whose two terminals are coupled to the configurable digital control circuit 210 via pins 116E and 116F. The digital control circuit 210 may include circuitry for sensing the voltage across the safety resistor 310, and if the sensed voltage exceeds a safety threshold, this may indicate that a short - circuit current is flowing through the digital current path. In such a case, the digital output circuit 210 may be configured to take action, such as opening switch 232 to stop the current flow and / or shutting down the configurable interface circuit 200 completely to prevent damage.
[0027] In Figure 2 and Figure 3 the example of, when the configurable interface circuit 200 operates in digital mode, there is no mechanism for measuring the digital current. In particular, the short - circuit clamping safety function does not actually measure the magnitude of the digital current, but only senses whether it is above or below the safety threshold. While in some cases measuring the digital current may not be required (e.g., the actual magnitude of the current is immaterial), in other cases it may be useful (e.g., for diagnostic purposes).
[0028] Digital currents are typically much larger than the analog currents that the configurable interface circuit 200 is configured to handle (analog currents are typically on the order of milliamperes, for example between -10 mA and 10 mA, or between -20 mA and 20 mA, or between -50 mA and 50 mA, while digital currents are typically on the order of amperes, for example up to 1 A, or up to 2 A). This means that it may be impractical to route the digital current through the sense resistor 112 and utilize the measurement circuit 106 without sacrificing the measurement accuracy of the analog current, or without using a rather expensive and power-consuming ADC within the measurement circuit 106. More specifically, the measurement circuit 106 needs to be able to measure currents up to the maximum value of the digital current, for example up to 1 A or 2 A, which is several orders of magnitude larger than the maximum / minimum value of the analog current. If an existing ADC used to measure analog currents in the range of -10 mA to 10 mA or -20 mA to 20 mA is subsequently used to measure a digital current up to 1 A or 2 A, the measurement resolution will be several orders of magnitude worse than that of an ADC used only for measuring analog currents. Alternatively, in order to maintain the same measurement resolution in the current range up to 1 A or 2 A, a more expensive and power-consuming ADC is required compared to the case where the measurement range is only -10 mA to 10 mA or -20 mA to 20 mA (for example, the sense resistor 112 needs to have a smaller resistance in order to accommodate a larger digital current while having a reasonable voltage drop across the sense resistor 112. The size of the LSB of the ADC needs to be very small, so the ADC needs to have very low noise in order to accurately measure, which may increase the size and power consumption of the ADC, which may be impractical). Therefore, it is impractical to route the digital current through the sense resistor 112.
[0029] Figure 4 Exemplary additional details of the configurable interface circuit 200 are shown, which is arranged to measure digital currents. The digital control circuit 210 includes an operational amplifier 410, which is arranged to sense whether the digital current exceeds a safety threshold. In this example, if the digital current is relatively low (and thus within the safe range), the voltage drop across pins 116E to 116F will be relatively low because there is only a small voltage drop across the safety resistor 310. However, if the digital current is relatively high (and thus may be a short-circuit current), the voltage drop across pins 116F to 116E will be relatively high due to the larger voltage drop across the safety resistor 310. If the voltage drop across pins 116E to 116F exceeds Vref (where Vref is a fixed reference threshold voltage relative to the voltage at pin 116E), the digital current is considered to have exceeded the safety threshold, and the output of the operational amplifier 410 will go high, thereby reducing the Vgs voltage of the FET 232, which limits the digital current during a short electrical short circuit, or changes the switch 232 to the off state during a long electrical short circuit.
[0030] The voltage across the safety resistor 310 is proportional to the digital current / voltage, so measuring a signal that depends on this voltage is a way to measure the digital current / current. However, the voltage across the safety resistor 310 is the "high-side" voltage, while the measurement circuit 106 is the "low-side" voltage. Therefore, in order to use the measurement circuit 106 to measure the voltage across the safety resistor 310 (which can save silicon area and cost compared to including an additional "high-side" measurement circuit), it is necessary to sense the voltage on both sides of the safety resistor 310 and transfer it to the low-voltage domain. To this end, in Figure 4 the example of, the digital control circuit 210 includes an operational amplifier 420 arranged as an amplifier, a resistor 422, and an FET 424, which are arranged to convert the voltage across the safety resistor 310 to the low-voltage domain. The converted voltage appears across the resistor 426, such that nodes 430A and 430B can be coupled to the input terminals of the ADC in the measurement circuit 106 to measure the converted current. Although this technique may be effective for measuring digital current / voltage, it requires additional circuitry, which both increases the cost of the configurable interface circuit 500 and the silicon area required for the digital control circuit 210.
[0031] Figure 5 An example configurable interface circuit 500 in accordance with one aspect of the present disclosure is shown. The configurable interface circuit 500 is similar to those described above, but includes additional functionality that can measure digital signals (digital current and / or digital voltage) with minimal additional cost and complexity. The configurable interface circuit 500 supports a variety of selectable operating modes (e.g., software configurable), including but not limited to analog mode and digital mode. The analog mode can include any one or more of the different selectable analog modes described previously, such as analog input current mode, analog output current mode, analog input voltage mode, analog output current mode. Thus, the analog control circuit 220 can operate in the same manner as described previously.
[0032] The configurable interface circuit 500 includes a first device terminal 120A that can be coupled to an external field device 130. It may also include a second device terminal 120B that can be coupled to the external field device 130, although this terminal can be a common terminal shared by many other devices / circuits, such that the second device terminal 120B is not actually part of the configurable interface circuit 500. The first device terminal 120A can take any form, such as a plug / socket, screw terminal, or any other form of conductive interface to which the external field device 130 can be electrically coupled.
[0033] The configurable interface circuit 500 also includes a digital current path, which is similar to the digital current path of the configurable interface circuit 200 (and may also optionally include the safety resistor 310), but further includes a digital sense resistor 510, whose first terminal is coupled to the first device terminal 120A. Thus, the digital current path in this example includes the switch 232, the diode 234, and the digital sense resistor 510 coupled in series, such that when operating in the digital output mode, digital current can flow through the devices constituting the digital current path. The body diode of the FET forming the switch 232 is also as Figure 5 shown, and its polarity direction is opposite to that of the diode 234. For simplicity and clarity, this feature is not shown in the subsequent drawings.
[0034] The configurable interface circuit 500 also includes an analog current path, which includes an analog sense resistor 512 having a first terminal coupled to the first device terminal 120A. The analog sensor resistor 512 is substantially the same as the sense resistor 112 described previously. It should be noted that both the digital sense resistor 510 and the analog sense resistor 512 are simple resistors, and the terms "digital sense" and "analog sense" are only used as labeling terms to indicate the purpose of each resistor (i.e., sensing a digital signal or sensing an analog signal), and they may also be referred to as the first sense resistor 510 and the second sense resistor 512.
[0035] The configurable interface circuit 500 also includes a measurement circuit 106, which is the same as the previously described one except that its input terminals are differentially connected to the current path. The first input terminal of the measurement circuit 106 is coupled to the second terminal of the digital sense resistor 510 (via the pin 116C), and the second input terminal of the measurement circuit 106 (via the pin 116B) is coupled to the second terminal of the analog sense resistor 512. As a result, the measurement circuit 106 is configured to measure the voltage between or across the second terminals of the digital sense resistor 510 and the analog sense resistor 512.
[0036] Finally, the configurable interface circuit 500 may include a configurable drive circuit 104, which includes a digital control circuit 210 and an analog control circuit 220, as described previously.
[0037] Figure 6Shows a visualization of the configurable interface circuit 500 operating in the analog measurement mode, where an analog current flows from the analog control circuit 220 to the field device 130 (and can be controlled by the analog control circuit - analog current output mode or the field device - analog current input mode). The analog current is represented by the arrow 600. It can be seen that the analog current 600 flows through the analog current path and the first device terminal 120A to reach the field device 130. In an alternative, for example, if the analog control circuit 220 is drawing current, the analog current 600 can flow in the opposite direction. During the analog operation mode, the configurable interface circuit 500 is configured to disable the digital output (e.g., because the digital control circuit 210 holds the switch 232 in the open state), such that no or negligible current flows from the power supply 240 through the digital current path. Additionally, no or negligible analog current will flow through the digital current path because in this example, due to the direction of the diode 234, the digital current path 234 presents a high impedance to the analog current. Also, the potential of the power supply 240 at one end of the digital current path may be higher than the potential of the first device terminal 120A, such that the analog current cannot flow through the digital current path. Thus, depending on the relative potential at which the configurable interface circuit 500 is designed to operate, the diode 234 can be optional. Additionally, the measurement circuit 106 is configured to present a high impedance at its first and second input terminals. The term "high" is intended to mean an impedance with no or negligible current flowing into the measurement circuit 106. The term "negligible" is intended to mean an electric current small enough for the following measurement functions to meet the accuracy requirements and may be on the order of microamps or less (e.g., single-digit microamps or lower, such as less than 10 microamps, or less than 5 microamps, etc.).
[0038] Since no or negligible current flows through the digital sense resistor 510, there will be no or negligible voltage drop across the digital sense resistor 510. As a result, the potential at the second terminal of the digital sense resistor 510 will be the same as (or substantially the same as if the current flowing through the resistor is negligible) the potential at the first end of the digital sense resistor 510. Thus, the voltage between the first input terminal and the second input terminal of the measurement circuit 106 will be the same as (or substantially the same as) the voltage across the analog sense resistor 512. Thus, in this operating mode, the measurement circuit 106 can accurately measure the analog signal. In some cases, for example, during the analog input current mode or the analog output current mode, the measured analog signal can be an analog current, which can be determined based on the measured voltage and the value of the analog sense resistor 512 (according to Ohm's law). Additionally or alternatively, during some other scenarios, for example, during the analog input or output voltage mode, the measured analog signal can indicate the analog voltage applied to the first device terminal 120A.
[0039] Figure 7Shows a visualization of the configurable interface circuit 500 operating in digital mode, where the digital current / voltage is controlled by the digital control circuit 210. The digital current 700 flows through the digital current path and the first device terminal 120A to the field device 130 (although it can also flow in the opposite direction depending on the specific circuit configuration used). During the digital operation mode, the analog control circuit 220 can be configured to present a high impedance to the analog current path, such that no or negligible current flows through the analog current path during the digital operation mode. Additionally or alternatively, the analog current path can include one or more components that can present a high impedance to the digital current, such as a diode, oriented such that its cathode is coupled to the second terminal of the analog sense resistor 512. In any case, due to the operation of the analog control circuit 220 and / or one or more components within the analog current path, the analog current path is configured to present a high impedance to the digital current.
[0040] Since no or negligible current flows through the analog sense resistor 512, there will be no or negligible voltage drop across the analog sense resistor 512. As a result, the electric potential at the second terminal of the analog sense resistor 512 will be the same as (or substantially the same as, if the current flowing through the resistor is negligible) the electric potential difference at the first terminal of the analog sense resistor 512. Therefore, the voltage between the first input terminal and the second input terminal of the measurement circuit 106 will be the same as (or substantially the same as) the voltage across the digital sense resistor 510. Thus, in this operation mode, the measurement circuit 106 can accurately measure the digital current, for example, by measuring the voltage and using the known resistance of the digital sense resistor 510 (according to Ohm's law). Additionally, or alternatively, the voltage at the first device terminal 120A (e.g., the digital voltage) can be determined by measuring the voltage at pin 116B in single-ended mode, or by measuring the voltage between the first and second terminals of the measurement circuit 106 and knowing the electric potential at the third device terminal 120C (i.e., the electric potential provided by the power supply 240) and the typical voltage drops of the switch 232 and the diode 234.
[0041] Thus, it can be seen that due to the addition of the digital sense resistor 510, a digital signal measurement function is added to the configurable interface circuit 500. The digital sense resistor 510 can be a discrete component, such as mounted on a PCB, or can be an integrated component within an integrated circuit (IC), such as the same IC that integrates the configurable drive circuit 104 and the measurement circuit 106 (and any one or more of the optional analog sense resistor 512, switch 232, and diode 234). In any case, it can be understood that the cost of the additional resistor is very low (e.g., around a few cents), especially considering that digital signal measurement may only be used for diagnostic purposes, does not require a high-precision resistor, and represents only very little additional circuit complexity. In addition, the existing measurement circuit 106 can be used without any redesign or change, and no additional pins are required on the IC that implements the drive circuit 104 and the measurement circuit 106, both of which greatly simplify the implementation of this additional feature.
[0042] The relative values of the analog sense resistor 512 and the digital sense resistor 510 can be set such that when operating in analog mode or digital mode, the voltage between the first input terminal and the second input terminal is within the operating range of the measurement circuit 106. In one example, they can be set such that the possible voltage range at the input terminals of the measurement circuit 106 is the same in both analog mode and digital mode, or such that the possible voltage ranges at the input terminals of the measurement circuit 106 in analog mode and digital mode are of the same order of magnitude. For example, typically the maximum value of the digital current is greater than the maximum value of the analog current. In this case, the resistance of the analog sense resistor 512 can be selected to be greater than the resistance of the digital sense resistor 510 such that the voltage across the input terminals of the measurement circuit 106 is similar regardless of whether a digital current or an analog current is being measured. In a specific non-limiting example, the configurable interface circuit 500 can be designed to control a digital current that varies between 0A and 1A and is designed to handle an analog current between -20mA and 20mA (e.g., if the configurable interface circuit 500 has a mode in which the analog current can flow into and out of the circuit). In this case, the resistance ratio of the analog sense resistor to the digital sense resistor can be set to 100:1, for example, the analog sense resistor 512 is 10 ohms and the digital sense resistor 510 is 0.1 ohm. This will result in a voltage range of 0 to 0.1V at the input terminals of the measurement circuit 106 when operating in digital mode and + / - 0.2V when operating in analog mode. Alternatively, the ratio can be set to 25:1, for example, the analog sense resistor 512 is 2.5 ohms and the digital sense resistor 510 is 0.1 ohm. This will result in a voltage range of 0.1V at the input terminals of the measurement circuit 106 when operating in either digital mode or analog mode.
[0043] Figure 8 An alternative implementation of the configurable interface circuit 500 according to another aspect of the present disclosure is shown. It can be seen that in this alternative, the circuit is configured to cause the digital current to flow in a direction opposite to that of the previous example. To this end, the direction / polarity of the diode 234 is reversed, and the switch 232 uses different components (specifically, an n-type FET). The FET forming the switch 232 has an inherent body diode whose orientation is opposite to the polarity direction of the diode 234 (much like Figure 5 as shown), although it is not shown in the figure for simplicity. In this example, the digital control circuit 210 controls the digital current 700 as described above, closing the switch 232 by controlling the gate voltage to allow current flow (e.g., digital "1"), and opening the switch 232 to stop current flow (e.g., digital "0"). When the switch 232 is in the off state, a high impedance is presented on the digital current path, such that no or negligible current can flow. Thus, by keeping the switch 232 open during the analog measurement mode, no or negligible current will flow through the digital current path. The diode 234 can be optionally omitted when the voltage at the device terminal 120A is equal to or higher than the voltage at the device terminal 120C (e.g., equal to or higher than ground).
[0044] Figure 9Shows a non - limiting example implementation of the analog control circuit 220 and the measurement circuit 106. It should be understood that these circuits can be implemented in a variety of different ways to achieve the above - described functions, and this is merely an exemplary implementation. Both the analog control circuit 220 and the measurement circuit 106 include optional line protectors 1042, 1044, 1046 coupled to pins 116B, 116C, and 116D to help present a high impedance to any current that may flow through pins 116B, 116C, and 116D into the analog current circuit 220 and the test circuit 106. However, due to the high impedance, these components can be omitted, otherwise these high impedances would be presented by the inputs of the operational amplifier buffers 1062, 1064 optionally included in the measurement circuit 106 and the output of the operational amplifier 1084 that is part of the analog current circuit 220. In this example, the measurement circuit 106 includes a gain stage 1066 (which can be configured to provide fixed or variable gain) to increase the magnitude of the voltage present between the inputs of the measurement circuit 106 before digital conversion by the ADC 1068. Thus, the ADC 1068 is configured to digitally convert a signal that depends on the voltage across the first and second input terminals of the measurement circuit 106. However, in an alternative, the gain stage 1066 can be omitted, and the ADC 1068 converts the voltage signal across the first and second input terminals of the measurement circuit 106. The ADC 1068 can be any suitable type of ADC 1068, such as a sigma - delta, pipelined, flash, etc. ADC, and is configured to output a digital value dig_meas, i.e., digitally convert the analog signal at its input.
[0045] The analog control circuit 220 in this example is configured to control and output an analog current and / or drive an output analog voltage. To this end, it includes a digital - to - analog converter DAC 1081, which is configured to receive a digital value dig_in and convert it into an analog signal. The digital value dig_in can be received from another entity / module (e.g., from software) and represents the desired analog signal. In this example implementation, the analog control circuit 220 includes a feedback loop formed by an operational - amplifier error amplifier 1084 and a feedback circuit 1082 that receives the signals present at the first and second input terminals of the measurement circuit 106. This may help maintain the desired analog signal output of the analog current circuit 220, although the feedback - loop circuit 1082 is optional. The operational - amplifier error amplifier 1084 is also configured to receive an on_off_ctrl signal, which can be used to turn off the analog control circuit 220 (e.g., when the configurable interface circuit 500 is operating in digital mode), although this can also be achieved in any other way, such as by using a control signal to turn off the DAC 1081.
[0046] The analog control circuit 220 may alternatively or additionally be configured to operate in a mode of receiving an analog current (e.g., provided by the field device 130), such as during an analog input current and / or voltage mode. Accordingly, a configurable bypass circuit may be included in the analog control circuit 220 and may be enabled during an analog input to couple the pin 116D to ground or a current sink. For simplicity, Figure 9 is not shown.
[0047] Those skilled in the art will readily understand that various changes or modifications can be made to the above aspects of the present disclosure without departing from the scope of the present disclosure.
[0048] The above term "coupled" includes a direct electrical connection between two components and an indirect electrical connection where two components are electrically connected to each other through one or more intermediate components.
[0049] In the analog operating mode, for an analog voltage input and an analog current input, it can be understood that, for example, the field device 130 can control the voltage or current in any desired manner. For example, it can be configured to control it digitally (e.g., turn it on and off to create digital "1"s and "0"s), but the configurable interface circuit 500 can still be considered to have an analog current flowing through an analog current path because, from the perspective of the configurable interface circuit 500, a certain amount of current can flow through the path and the analog current and / or analog voltage are measurable as described above regardless of the purpose of the field device 130 for controlling the received current.
[0050] In the above example, the measurement circuit 106 includes an ADC for measuring the voltages at the pins 116B and 116C. However, in an alternative, the measurement circuit 106 may not include an ADC but may include terminals to which an external ADC can be connected to measure the voltages present at the pins 116B and 116C. In such a case, it may include one or more buffers and output terminals to be able to connect the external ADC to measure the voltage across the second terminals of the digital sense resistor 510 and the analog sense resistor 512. Thus, regardless of whether the measurement circuit 106 itself includes an ADC, it is still suitable for measuring the voltage between the pins 116B and 116C, either using the ADC within the measurement circuit 106 or allowing the connection of an external ADC.
[0051] Aspects of the present disclosure
[0052] Non-limiting aspects of the present disclosure are listed in the following numbered clauses:
[0053] 1. A configurable interface circuit supporting alternative operating modes, including an analog mode and a digital mode, the interface circuit comprising:
[0054] Device terminals that can be coupled to external field devices;
[0055] A digital current path, coupled to the device terminals, wherein the digital current path includes a digital sense resistor having a first terminal coupled to the device terminals; and
[0056] An analog current path, including an analog sense resistor, the analog sense resistor having a first terminal coupled to the first terminal of the digital sense resistor;
[0057] Wherein when the configurable interface circuit operates in analog mode, an analog current can flow through the analog current path and the device terminals, and an analog signal can be measured by measuring the voltage between the second terminal of the digital sense resistor and the second terminal of the analog sense resistor, and
[0058] Wherein when the configurable interface circuit operates in the digital mode, a digital current is controlled to flow through the digital current path and the device terminals, and a digital signal can be measured by measuring the voltage between the second terminal of the digital sense resistor and the second terminal of the analog sense resistor.
[0059] 2. The configurable interface circuit according to clause 1, wherein the resistance of the analog sense resistor and the resistance of the digital sense resistor are such that when the configurable interface circuit operates in the analog mode or the digital mode, the voltage between the first input terminal and the second input terminal is within the operating range of the measurement circuit.
[0060] 3. The configurable interface circuit according to any of the preceding clauses, wherein the maximum value of the digital current is greater than the maximum value of the analog current, and
[0061] Wherein the resistance of the analog sense resistor is greater than the resistance of the digital sense resistor.
[0062] 4. The configurable interface circuit according to any of the preceding clauses, wherein the digital sense resistor is a discrete component.
[0063] 5. The configurable interface circuit according to any of the preceding clauses, wherein the digital current path further includes a switch, and wherein the configurable interface circuit further includes:
[0064] A digital control circuit, coupled to the switch, and configured to control the digital current by controlling the state of the switch when the configurable interface circuit operates in the digital mode.
[0065] 6. The configurable interface circuit according to clause 5, wherein when the configurable interface circuit operates in the analog mode, the digital drive circuit is configured to keep the switch in an off state.
[0066] 7. The configurable interface circuit according to clause 5 or clause 6, wherein the switch includes a transistor.
[0067] 8. The configurable interface circuit according to any of the preceding clauses, wherein when the configurable interface circuit operates in the analog mode, the configurable interface circuit is configured to present a high impedance to the analog current at the digital current path.
[0068] 9. The configurable interface circuit according to clause 8, wherein the digital current path further includes a diode arranged such that when the configurable interface circuit operates in the digital mode, the digital circuit can conduct current through the digital current path, and when the configurable interface circuit operates in the analog mode, the diode blocks the analog current from flowing through the data current path.
[0069] 10. The configurable interface circuit according to any of the preceding clauses, wherein when the configurable interface circuit operates in the digital mode, the configurable interface circuit is configured to present a high impedance to the digital current at the analog current path.
[0070] 11. The configurable interface circuit according to any of the preceding clauses, further comprising a measurement circuit for measuring the voltage between the second terminal of the digital sensing resistor and the second terminal of the analog sensing resistor, the measurement circuit comprising:
[0071] A first input terminal coupled to the second terminal of the digital sensing resistor; and
[0072] A second input terminal coupled to the second terminal of the analog sensing resistor.
[0073] 12. The configurable interface circuit according to clause 11, wherein the measurement circuit includes an analog-to-digital converter ADC configured to digitally convert a signal depending on the voltage between the first input terminal and the second input terminal.
[0074] 13. The configurable interface circuit according to any of the preceding clauses, wherein the digital current path is coupleable to an external power source for providing or absorbing digital current.
[0075] 14. The configurable interface circuit according to any of the preceding clauses, wherein the analog current is provided by the external field device.
[0076] 15. The configurable interface circuit according to any one of clauses 1 to 13, further comprising:
[0077] An analog control circuit, coupled to the analog current path, wherein the analog voltage is controlled by the analog control circuit.
[0078] 16. The configurable interface circuit according to any of the preceding clauses, wherein the measurement circuit is implemented within an integrated circuit.
[0079] 17. The configurable interface circuit according to any of the preceding clauses, wherein the analog signal includes the analog current.
[0080] 18. The configurable interface circuit according to any of the preceding clauses, wherein the analog signal includes the input voltage at the device terminal.
[0081] 19. The configurable interface circuit according to any of the preceding clauses, wherein the digital signal includes the digital current.
[0082] 20. The configurable interface circuit according to any of the preceding clauses, wherein the digital signal includes the digital voltage at the device terminal.
[0083] 21. A method for operating a configurable interface circuit in any one of a plurality of selectable operating modes, including an analog mode and a digital mode, wherein the configurable interface circuit includes:
[0084] Device terminals that can be coupled to an external field device;
[0085] A digital current path, coupled to the device terminals, wherein the digital current path includes a digital sense resistor having a first terminal coupled to the device terminals;
[0086] An analog current path, including an analog sense resistor having a first terminal coupled to the first terminal of the digital sense resistor; and
[0087] A measurement circuit, including:
[0088] A first input terminal, coupled to the second terminal of the digital sense resistor; and
[0089] A second input terminal, coupled to the second terminal of the analog sense resistor,
[0090] wherein the method includes:
[0091] When the configurable interface circuit is operating in analog mode and an analog current can flow through the analog current path:
[0092] Measuring an analog signal by the measurement circuit by measuring the voltage between the first input terminal and the second input terminal, and
[0093] When the configurable interface circuit operates in digital mode and a digital current can flow through the digital current path:
[0094] A digital signal is measured by measuring the voltage between a first input terminal and a second input terminal through a measuring circuit.
[0095] 22. An interface circuit supporting multiple selectable operation modes, the interface circuit comprising:
[0096] Device terminals that can be coupled to an external field device;
[0097] A first current path, coupled to the device terminals, wherein the first current path includes a first sensing resistor having a first terminal coupled to the device terminals; and
[0098] A second current path, including a second sensing resistor having a first terminal coupled to the first terminal of the first sensing resistor;
[0099] Wherein when the interface circuit operates in a first mode in which a first current can flow through the first current path, the interface line is configured to measure a first signal by measuring the voltage between a second terminal of the first sensing resistor and a second terminal of the second sensing resistor, and
[0100] Wherein when the interface circuit operates in a second mode in which a second current can flow through the second current path, the interface line is configured to measure a second signal by measuring the voltage between a second terminal of the first sensing resistor and a second terminal of the second sensing resistor.
[0101] 23. The interface circuit according to clause 22, wherein the maximum possible value of the first current is greater than the maximum possible value of the second current.
[0102] 24. The interface circuit according to clause 22 or clause 23, wherein the resistance of the first sensing resistor is less than the resistance of the second sensing resistor.
[0103] 25. The interface circuit according to any one of clauses 22 to 24, wherein the first mode is a digital mode and the second mode is an analog mode.
[0104] 26. The interface circuit according to any one of clauses 22 to 25, wherein the first signal is a first current and the second signal is a second current.
Claims
1. A configurable interface circuit supporting an optional operating mode, including an analog mode and a digital mode, the interface circuit comprising: Device terminals couplable to an external field device; A digital current path coupled to the device terminals, wherein the digital current path includes a digital sense resistor having a first terminal coupled to the device terminals; And An analog current path including an analog sense resistor having a first terminal coupled to the first terminal of the digital sense resistor; Wherein, when the configurable interface circuit operates in the analog mode, an analog current can flow through the analog current path and the device terminals, and an analog signal can be measured by measuring the voltage between the second terminal of the digital sense resistor and the second terminal of the analog sense resistor, and Wherein, when the configurable interface circuit operates in the digital mode, a digital current is controlled to flow through the digital current path and the device terminals, and a digital signal can be measured by measuring the voltage between the second terminal of the digital sense resistor and the second terminal of the analog sense resistor.
2. The configurable interface circuit according to claim 1, wherein the resistance of the analog sense resistor and the resistance of the digital sense resistor are such that when the configurable interface circuit operates in the analog mode or the digital mode, the voltage between the first input terminal and the second input terminal is within the operating range of the measurement circuit.
3. The configurable interface circuit according to claim 1, wherein the maximum value of the digital current is greater than the maximum value of the analog current, and Wherein the resistance of the analog sense resistor is greater than the resistance of the digital sense resistor.
4. The configurable interface circuit according to claim 1, wherein the digital sense resistor is a discrete component.
5. The configurable interface circuit according to claim 1, wherein the digital current path further includes a switch, and wherein the configurable interface circuit further includes: A digital control circuit coupled to the switch and configured to control the digital current by controlling the state of the switch when the configurable interface circuit operates in the digital mode.
6. The configurable interface circuit according to claim 5, wherein when the configurable interface circuit operates in the analog mode, the digital drive circuit is configured to hold the switch in an open state.
7. The configurable interface circuit according to claim 1, wherein when the configurable interface circuit operates in the analog mode, the configurable interface circuit is configured to present a high impedance to the analog current at the digital current path.
8. The configurable interface circuit according to claim 7, wherein the digital current path further includes a diode arranged such that when the configurable interface circuit operates in the digital mode, the digital current can flow through the digital current path, and when the configurable interface circuit operates in the analog mode, the analog current is blocked from flowing through the data current path by the diode.
9. The configurable interface circuit according to claim 1, wherein when the configurable interface circuit operates in the digital mode, the configurable interface circuit is configured to present a high impedance to the digital current at the analog current path.
10. The configurable interface circuit according to claim 1, further comprising a measurement circuit for measuring the voltage between the second terminal of the digital sense resistor and the second terminal of the analog sense resistor, the measurement circuit comprising: a first input terminal coupled to the second terminal of the digital sense resistor; and a second input terminal coupled to the second terminal of the analog sense resistor.
11. The configurable interface circuit according to claim 1, wherein the measured analog signal includes the analog current.
12. The configurable interface circuit according to claim 1, wherein the measured analog signal includes the input voltage at the device terminal.
13. The configurable interface circuit according to claim 1, wherein the measured digital signal includes the digital current.
14. The configurable interface circuit according to claim 1, wherein the measured digital signal includes the digital voltage at the device terminal.
15. A method for operating a configurable interface circuit in any one of a plurality of selectable operating modes, including an analog mode and a digital mode, wherein the configurable interface circuit comprises: device terminals couplable to an external field device; a digital current path coupled to the device terminals, wherein the digital current path includes a digital sense resistor having a first terminal coupled to the device terminals; and an analog current path including an analog sense resistor having a first terminal coupled to the first terminal of the digital sense resistor; wherein the method comprises: when the configurable interface circuit operates in the analog mode and an analog current can flow through the analog current path: measuring an analog signal by measuring the voltage between the second terminal of the digital sense resistor and the second terminal of the analog sense resistor, and when the configurable interface circuit operates in the digital mode and a digital current can flow through the digital current path: measuring a digital signal by measuring the voltage between the second terminal of the digital sense resistor and the second terminal of the analog sense resistor.
16. An interface circuit supporting multiple selectable operating modes, the interface circuit comprising: device terminals couplable to an external field device; a first current path coupled to the device terminals, wherein the first current path includes a first sense resistor having a first terminal coupled to the device terminals; and a second current path including a second sense resistor having a first terminal coupled to the first terminal of the first sense resistor; When the interface circuit operates in the first mode, a first current can flow through the first current path, and the interface circuit is configured to measure a first signal by measuring a voltage between a second terminal of the first sensing resistor and a second terminal of the second sensing resistor, and when the interface circuit operates in the second mode, a second current can flow through the second current path, and the interface circuit is configured to measure a second signal by measuring a voltage between a second terminal of the first sensing resistor and a second terminal of the second sensing resistor.
17. The interface circuit according to claim 16, wherein a maximum possible value of the first current is greater than a maximum possible value of the second current.
18. The interface circuit according to claim 16, wherein a resistance of the first sensing resistor is less than a resistance of the second sensing resistor.
19. The interface circuit according to claim 16, wherein the first mode is a digital mode and the second mode is an analog mode.
20. The interface circuit according to claim 16, wherein the first signal is a first current and the second signal is a second current.